Thirty cases showing hard discs were collected from 206 consecutive cases of posterior disk herniation duringthe past one and a half years period. According to the shape of hard disc and the presence of marginal bone defect(MBD) of vertebral end plate, 30 cases could be categorized into 4 distinct groups. They were small hard disc withfocal MBD(group 1), lage hard disc with broad based MBD(group 2), hard disc seperated from vertebral body withoutMBD(group3) and hard disc fused with vertebral body without MBD(group 4). There were 14 patients in group 1. Inall but one case, the hard discs and MBDs were located at the paramedial aspect of the posterior margin of the endplate, Ten(76.9%) of thewe had Schmorl's nodes and these were considered to represent an avulsion from theweakened bone margin as the disk herniated acutely. The posterior longitudinal ligament seemed to have preventeddetachement of the bony fragment. Group 2 included 2 patients and CT findings as well as plain X-ray features wereidentical to a limbus vertebra. This was considered to represent passive displacement of bony fragment by theintravertebral herniation of the disk. Nine patients belonged to group 3 and represent dystrophic calcification ofherniated disk. Group 4 include 5 patients and was disclosed as a simple osteophyte. From our study, it wasconcluded: (1) that the hard disc seen in lumbar CT scan was probably the results of the detachment of a bonefragment from the vertebral end plate which has an underlying weak area due to the herniated disc as well as acalcification of osteophyte formation and (2) specific terms(avulsed fragment, limbus vertebra, calcification orspur formation ) is more preferable to use than hard disc which is inaccurate.